1. Field of the Invention
The present invention relates generally to a machine vise for clamping a workpiece, and more particularly a machine vise equipped with a device for detecting a clamping force exerted on the workpiece.
2. Discussion of the Prior Art
A commonly known machine vise has (a) a body having a stationary jaw fixed thereto, (b) a movable member having a movable jaw fixed thereto, and movable relative to the body, (c) a support portion formed on one of the body and the movable member, (d) an internally threaded member provided fixedly to the other of the body and the movable member, and (e) a feedscrew member rotatably supported by the support portion, and engaging the internally threaded member, for moving the movable member relative to the body by a rotating motion thereof, to clamp a workpiece between the stationary jaw of the body and the movable jaw of the movable member.
A conventional machine vise is not equipped with a device which indicates a clamping force which is actually exerted on the workpiece between the stationary and fixed jaws. The optimum clamping force that should be applied to the workpiece differs depending upon the specific material and configuration of the workpiece, and upon the particular type of work to be performed on the workpiece. However, the clamping force on the conventional machine vise is determined by his expertise or operator, relying upon the experience. Accordingly, the clamping force applied the workpiece may be excessive or insufficient, resulting in damaging the workpiece, or a failure to machine or otherwise process the workpiece as contemplated.
In light of the above inconvenience, the assignee of the present application proposed a machine vise wherein one of the stationary and movable jaws is equipped with a detector device for sensing the clamping force acting on the workpiece, as disclosed in Publication No. 61-3586 (published for opposition purpose) of Japanese Utility Model Application. In the proposed arrangement, the clamping force may be easily adjusted based on the value obtained by the detector device, whereby the conventionally experienced inconveniences of excessive or insufficient clamping of the workpiece may be suitably avoided.
More specifically described, the detector device consists of a pair of generally cylindrical, parallel strain members which are elastically deformable when subjected to an axial force applied thereto upon clamping of the workpiece between the stationary and movable jaws via respective mouthpieces. Each of the strain members is provided with a strain gage bonded thereto. The strain members are substantially entirely accommodated within parallel holes formed in the movable jaw, such that the strain members are secured at their one end to the movable jaw while their other end is held in abutting contact with the mouthpiece for the movable jaw. In this arrangement, the mouthpiece for the movable jaw must be disposed so that the mouthpiece is movable relative to the movable jaw in the clamping direction, in order to permit the strain members to be elastically deformed when the workpiece is clamped. Therefore, it has been difficult to provide this type of arrangement on a highly precise machine vise which requires high levels of parallelism between the mouthpieces for the stationary and movable jaws, and squareness of the mouthpieces to the clamping direction (to the top surface of the body on which the movable member is slidably moved). In a machine vise wherein mouthpieces are connected to the jaws so as to permit relative movement, there is a tendency to produce a reaction, force as a result of clamping the workpiece which is unevenly exerted to the clamping surfaces of the mouthpieces, with local portions of the mouthpieces being subjected to a greater forces than the other portions. Consequently, the parallelism of the mouthpieces, and their squareness to the clamping direction tend to be easily deteriorated. Namely, machine uses requiring high degrees of such parallelism and squareness of the mouthpieces proposed has made use of structures such as the detector device difficult.
Further, uneven distribution of the reaction force on the mouthpiece for the movable jaw causes different magnitudes of elastic deformation or strain of strain members disposed between the mouthpiece and the movable jaw, thereby lowering the sensing accuracy or reliability of the detector device.